Field of the Invention
This disclosure relates to a method of making a flexible magnetized sheet. More particularly, this disclosure relates to a method of making a flexible magnetized sheet using cold extrusion and electron beam curing.
Description of the Related Art
Flexible magnetic sheets are known in the art. A typical method of making a flexible magnetic sheet involves extruding a molten mixture of magnetizable particles (such as iron oxide) suspended in a polymeric binder at an elevated temperature at least as high as the melting point of the polymer, passing the hot melt through a magnetic field to magnetically orient the iron oxide particles, and then cooling the sheet to solidify the binder and “freeze” the particles so that they are unable to shift from their magnetic orientation.
The extrusion step may be done using a slot die and may include co-extruding the magnetizable sheet onto a substrate such as paper. The magnetizing step may be accomplished by running the molten sheet over a magnetic roller. The cooling step may be accomplished by passing the still molten sheet over a cooling roller. The use of ultraviolet (UV) radiation has been tried as a means of solidifying the polymeric binder but has failed due to the opacity of the sheet.
The extrusion die is kept at an elevated temperature which has several disadvantages. Heating the die requires energy. Heating the die results in a molten mixture that begins to cure as it cools, limiting the ability to orient the suspended magnetic particles. And heating the die can decrease the die's useful life.
The present disclosure addresses these disadvantages.